Apple is testing an iPhone 6 with a screen resolution of 1704 x 960 pixels - but the size of the screen remains a mystery.Reuters

iPhone rumours in the tech blogosphere are like opinions. Everyone's got a different one to roll out, and for the most part they're all rubbish.

The barrage of iPhone 6 rumours has been steadily increasing in recent weeks with the usual array of leaks, blurry pictures, mockups and spurious supply-chain sources.

Today however we have something which we can put a but more trust in. Mark Gurman from 9to5Mac is a reporter who has deep links within the company and the wider community around Apple and its products, including developers and engineers - meaning that when he says something about the next iPhone, it's probably worth listening.

He is reporting that sources briefed on Apple's plans for the iPhone 6 tell him that the company will be making a big jump in resolution with its next iPhone, something it last did when it moved from the iPhone 4S' 3.5in screen to the iPhone 5's 4in screen.

At least one of the versions of the iPhone 6 Apple is testing (it is rumoured to be looking at several larger sized iPhones) will have a pixel tripling mode, meaning the resolution will be three times what is known as the "base resolution" for the iPhone 5s and iPhone 5c.

1704 x 960 pixels

To understand all the intricacies of iPhone resolutions and graphical scaling, you should refer to the original article, but for the sake of brevity, if you understand that the base resolution of the iPhone 5 is 568 pixels vertically by 320 pixels horizontally, then the new iPhone 6 will have its resolution tripled, to give you a new resolution of 1704 x 960 pixels.

Comparison of the iPhone 5s screen resolution and the larger iPhone 6 resolution.9to5Mac.com

Apple's original iPhone's 3.5in screen had a resolution of just 480 x 320 pixels, which was doubled to 640 x 960 pixels on the iPhone 4, heralding the era of the Retina display (Apple give anything with a pixel density above 300 pixels per inch (ppi) the title Retina).

In 2012 Apple introduced the iPhone 5, which increased the phone's screen size to 4in diagonally. It achieved this by increasing the height of the screen to 1136 pixels while retailing the 640 pixel width.

By tripling the iPhone 5's base resolution it would mean the iPhone 6 screen would retain the same 16:9 aspect ratio seen on Apple's phones since the iPhone 5.

4.7in or 5.5in?

Gurman doesn't speculate about the specific size of the iPhone 6 but says that information from his sources and evidence from leaked iPhone 6 parts suggest the next smartphone from Apple will have a screen that is both taller and wider.

However the two most speculated iPhone 6 screen sizes are 4.7in and 5.5in with Apple likely at one point testing both of these.

If the higher screen resolution is applied to the 4.7in screen we get a pixel density of 416ppi which is close to the pixel density of the current crop of high end Android devices, including the Samsung Galaxy S5 (431ppi) and the HTC One (440ppi).

Applying the resolution to a 5.5in screen however gives a pixel density of 356ppi, which is lower than the Android competition but still in Retina territory.

Developers

Speaking about what the changes in resolution and screen size mean for the iOS software running on the device, the sources speaking to Gurman said "iOS functions like the Home screen, Notification Center, and Settings panels, will simply appear like larger versions of those functions on the current iPhone display."

Developers would obviously need to update their apps, but the direction iOS design took with iOS 7 means that updates should be easier, and some could even be automatic thanks to a reliance on raster graphics.

The iPhone 6 will also come with an A8 chip which sources say will focus on improving performance and getting more out of the battery rather than making big core architectural changes.

While Apple's developer conference WWDC is just weeks away, that will focus on software (iOS 8 and Mac OS X 10.10) with announcements about a new iPhone not coming until August with a release predicted for September.

Earlier, German website ifun reported that local Apple Store staff had been prevented from taking any holidays during September while no restrictions were in place for August - suggesting an August announcement and September release.